Marcasite is characterized by twinned or stalactitic form with radiating fibers. It has a color of pale bronze-yellow to almost white and exhibits metallic luster. It has a hardness of 6-6.5 in Mohs Scale of Hardness and a specific gravity of 4.9. This sample has a measurement of 14.45 cm. long, 14.1 cm. wide and 7.8 cm. thickness.

Marcasite is an iron sulfide and is identical with pyrite, the most widespread sulfide mineral found in metalliferous vein. It is less stable than pyrite, being easily decomposed, and is not common. It is deposited at low tempe-rature (less than 450 oC) from acid solution and found in near-surface deposits, most commonly in sedi-mentary rocks such as limestone, especially chalk, and clay, as single crystals, concretions or as a replacement of fossils.

Marcasite is used to a slight extent as a source of sulfur. It can also be cut and polished for ornaments.

The specimen was collected in Brgy. Narra, San Marcelino, Zambales. It was acquired by the National Museum as a donation from Benguet Corp.-DCO on December 16, 1996 having an accession no. NMM-714. The name comes from the Arabic word once used for pyrite.